Thermodynamical detection of hydrophobic hydration of tris(2,4-pentanedionato)-cobalt(III) and tris(3,5-heptanedionato)cobalt(III) in water

Abstract

YASUIU YOSHIMURA. Can. J. Chem. 69, 1388Chem. 69, (1991. The solubilities of tris(2,4-pentanedionato)cobalt(III) and tris(3,S-heptanedionato)cobalt(III) in water, heptane, and 1,2-ethanediol were determined over the temperature range 5-50°C and from these data the thermodynamic quantities of solution at 25°C were estimated. The free energy (AG:), enthalpy (AH:), and entropy (AS:) of transfer of these chelates from heptane to some solvents were calculated from the corresponding thermodynamic quantities of solution. When AH: and AS: were separately plotted against AG:, the data of transfer from heptane to water deviated markedly from a correlation obtained for the data of transfer to the solvents other than water. This finding indicates that these chelates are subject to hydrophobic hydration in their aqueous solutions. The solubility of tris(glycinato)cobalt(III) in water was also determined over the temperature range 540°C and its temperature dependence of the solubility is compared with that for the cobalt(II1) chelates of the P-diketones.Key words: tris cobalt(II1) chelates of P-diketones and glycine, temperature dependence of solubility, thermodynamic parameters of solution, thermodynamic parameters of transfer, hydrophobic hydration. Mots clis : chklates de tris cobalt(II1) de P-dicttones, influence de la temptrature sur la solubilitt, paramttres thermodynamiques de solution, pararnbtres thermodynamiques de transfert, hydratation hydrophobe.[Traduit par la rtdaction]The author has investigated through solubility measurements a dissolution behavior of tris(2,4-pentanedionato)cobalt(III) ( C~( a c a c )~) in the aqueous mixed solvents of dimethyl sulfoxide (DMSO) (I), 1,4-dioxane (D) (2), 2-methyl-2-propanol (TBA) (2), 2-butoxyethanol (BE) (3), and 2-ethoxyethanol (EE) (3). The enthalpy (AH!) and entropy of solution (AS!) for Co(acac)3 in water estimated from temperature dependence of the solubility are negative (1) and its heat capacity of solution (AC:,) is positive (2). It has been extensively found that nonpolar nonelectrolytes dissolve in water with negative AH! and AS! , and with positive AC;,, (see, for example, ref. 4). This finding is explained in terms of hydrophobic hydration. Thus Co(acac)3 seems to behave as a hydrophobic solute in water. For alkanes which are typically hydrophobic nonelectrolytes their hydrophobic properties increase with an increase in number of carbon atoms (5). From an analogy, the substitution of alkyl groups for two terminal methyl groups of 2,4-pentanedione (acac) in Co(acac)3 is expected to increase the hydrophobic property.The hydrophobic hydration is brought about by an effect of hydrophobic solutes on the hydrogen-bonded network structure of water and is phenomenon characteristic of aqueous solution (68). To make sure that metal chelates such as Co(acac)3 are subject to the hydrophobic hydration, their thermodynamic quantities of solution in water need to be compared with those in some solvents other than water. This confirmation seems to provide useful information in...

A Study on the Development of CVD Precursors VI-Thermal Properties of Co(III) β-Diketonates

“…All complexes are already known and melting points of these complexes are relatively high for the possible precursors. However, Co(hd)3 as first reported by Yoshimura 14 showed the melting point is unusually low (53. ) for the Co precursors and this could be used as a potential CVD/ALD precursor even though this has not been used so far.…”